MEMOIR OF DELAMBRE. 127 
be subjected to the mathematical laws of gravitation ; its course and the places 
which it had occupied in the heavens were susceptible of demonstration. It 
was thus ascertained that it had been before observed by different astronomers, 
who had not, however, distinguished it from the fixed stars. Delambre under- 
took the preparation of tables respecting its movements, and published them 
without delay, presenting with great exactness all the observations which had 
been made up to that time. The Academy of Sciences had proposed this sub- 
ject for one of its annual prizes, and bestowed its suffrage on the work of De- 
lambre. <A striking attestation was herein afforded to the precision of the new 
astronomical methods; for though Herschel’s planet had described but a tenth 
part of its course since its discovery, its movements were determined with as 
much exactness as those of other planets, our knowledge of which ascends to 
periods of remote antiquity. 
To Delambre we owe also those tables of the sun which were published at 
the same time ; as likewise those of Jupiter and Saturn. He undertook further 
to construct ecliptic tables of the satellites of Jupiter, and completed this arduous 
and immense labor in a few years. 
The object of astronomical tables is to represent the actual state of the heavens 
at a given moment. They proceed upon the general principle of the stability 
of natural laws, and from the past enable us to attain a knowledge of the future. 
These researches are guided by geometry, which was said by Plato to have its 
abode in the heavens. They are controlled also by other mathematical theories 
which the moderns have invented, and which have served to detect the causes 
and the laws of celestial movements. 
The most general phenomena, it was first perceived, were necessary conse- 
quences of the mathematical laws of gravitation ; still later, more precise observa- 
tions indicated irregularities in the course of certain heavenly bodies, which did 
not appear to result from the general laws. It was asked if the resistance of 
an etherial medium might not affect the planetary movements; if gravitation 
was as simple in its action as had been supposed ; if the transmission of its force 
was instantaneous or progressive, like that of light. These doubts no longer 
exist, and it was in the bosom of this Academy that they were resolved. The 
inequalities which seemed inexplicable are necessary results of a mutual action 
between the celestial bodies ; they are no exceptions to the mathematical laws 
of gravity, which, on the contrary, they serve to confirm. The planctary world 
ozcillates between limits which it cannot transcend; it contains within itself 
principles of stability and duration which suftice to govern and preserve it. It 
was the imperfection of knowledge alone which led astronomers to have recourse 
to occasional compensatory causes. ‘The more the universe has been studied, 
the more admirable have appeared the unity and simplicity of its laws. Never 
have the sciences attained perfection without evincing the immutable order which 
an infinite wisdom has impressed on all its works. 
All these momentuous questicns respecting the system of the world were under 
discussion when Delambre gave himself with characteristic ardor to the study 
of astronomy. He assisted at the sitting of the Academy when Laplace com- 
municated his important discoveries on the respective inequalities of Jupiter and 
Saturn, and at once conceived the design of applying the results of that profound 
analysis to perfect the tables of those two planets. 
To collect and discuss all the observations which have been taken, so as to 
render them comparable with one another and with the results of scientific 
theory; to distinguish, by this means, the elements proper to be employed, and 
to assign to those elements the value due to them in reconciling the theorems of 
analysis with the observed facts; such is, in general, the succession of steps to 
be followed in the construction of astronomical tables. 
Delambre applied himself especially to those of the sateilites of Jupiter—an 
undertaking so arduous, and of such vast extent, that nothing i-ss than the two 
